The present invention relates to a cylinder apparatus of a sheet-fed rotary press which transfers an image from a plate mounted on a plate cylinder to a blanket cylinder and further transfers the image to a sheet.
A blanket to blanket perfecting press is known as one type of sheet-fed printing press, wherein images are transferred from blanket cylinders to upper and lower surfaces of the sheet while the sheet passes between the blanket cylinders. The printing press of this type has upper and lower blanket cylinders which are brought into rolling contact with each other, and upper and lower plate cylinders respectively brought into rolling contact with the upper and lower blanket cylinders. One of the upper and lower blanket cylinders has grippers for receiving the sheet from a preceding transfer cylinder and then transferring same to a subsequent one.
FIG. 1 is a longitudinal sectional view of a cylinder apparatus of a conventional blanket to blanket perfecting press. Referring to FIG. 1, a printing plate 3 is mounted on a plate cylinder 1, and each end of the printing plate 3 is held by a plate lock up device 2 in a notch of the plate cylinder 1. A blanket 5 is mounted on a blanket cylinder 4 held in rolling contact with this plate cylinder 1, and each end of the blanket 5 is held by a metal member 6 disposed in a recess of the blanket cylinder 4. A gripper unit 9 having grippers 7 and gripper pads 8 is mounted inside the recess of the blanket cylinder 4 to transfer the sheet from the grippers of the upstream transfer cylinder to the grippers of the downstream transfer cylinder. The plate and blanket cylinders 1 and 4 are rotated along directions indicated by arrows A and B, respectively. Upon rotation of these cylinders, an image is transferred from the printing plate 3 to the blanket 5. The image is then transferred to the sheet passing between this blanket cylinder 4 and the lower blanket cylinder 4, thereby performing printing.
In the conventional cylinder apparatus as described above, when ink is applied to an image portion of the printing plate from form rollers in an inking unit, each of the form rollers abuts against the leading edge of the printing plate 3 so that the ink is applied thereto, as indicated by reference numeral 10. When the ink at the leading edge is transferred to the sheet, the sheet is contaminated. In this case, when phases of the cylinders 1 and 4 are slightly shifted along the circumferential direction in the broadside printing press so that the leading edge of the printing plate 3 which is applied with the ink opposes the notch in the blanket cylinder 4, the above problem can be solved. However, in the perfecting press, the grippers 7 interfere with such a phase shift between the cylinders 1 and 4. Therefore, in the conventional perfecting press, the sheet tends to be contaminated, thereby degrading the printing quality and producing spoilage.